1. Field of the Invention
This invention is directed to solid electrolytes containing additives including a toughening agent and/or a basic sink material and, in particular, to solid electrolytes containing a polymeric matrix, a salt, a solvent, and said additives. The toughening agent imparts mechanical strength to the solid electrolyte and the basic sink removes or traps acids (e.g., HF) in the solid electrolyte.
2. State of the Art
Electrolytic cells containing an anode, a cathode and a solid solvent-containing electrolyte incorporating a salt are known in the art and are usually referred to as "solid batteries". See, for instant, U.S. Pat. Nos. 5,229,225, 5,238,758, 5,358,801, and 5,366,928. These cells offer a number of advantages over electrolytic cells containing a liquid electrolyte (i.e., "liquid batteries") including improved safety features.
Solid batteries employ a solid electrolyte interposed between a cathode and an anode. The solid electrolyte contains either an inorganic or an organic matrix and a suitable salt, such as an inorganic ion salt, as a separate component. Electrolytic cells containing a solid electrolyte having a polymeric matrix suffer from low ion conductivity and, accordingly, in order to maximize the conductivity of these materials, the matrix is generally constructed as a very thin film, i.e., in the range of about 25 to about 250 .mu.m. Minimizing the thickness of the film reduces the total amount of internal resistance within the electrolyte but also decreases the solid electrolyte's structural integrity. In addition, good adherence of the anode and cathode to the solid electrolyte is necessary for optimum operation of electrochemical cells made therefrom.
Another problem encountered in electrolytic cells is the presence of impurities such as acids (e.g., HF) in the solid and liquid electrolytes. HF is derived from certain lithium salts (e.g., LiPF.sub.6) that are employed. For example, LiPF.sub.6 reacts with water to form HF, LiF (insoluble) and other by-products, thereby reducing the amount of salt available. The acids adversely effect electrochemical performance.
In view of the above, the art is in need of solid electrolytes having superior mechanical attributes, including toughness, hardness, and resiliency. In addition, the solid electrolyte should also adhere to the anode and cathode layers of the electrolytic cell to minimize internal resistance and increase electrochemical performance. Furthermore, there is a need to reduce or eliminate acidic impurities in the solid electrolyte.